Had Onan not spilled his seed upon the ground, he might have invented invisible ink. The possibility had not occurred to me until I read this account of the start of Britain’s intelligence services. Even then the implications seemed so startling as to be barely credible — that the entire trade in espionage, including the serried ranks of Cheltenham’s GCHQ, the massed battalions at Fort Meade’s National Security Agency, the MI5s, 6s and other shadowy digits, not to mention literature’s denizens, from Ashenden and Greenmantle to James Bond and George Smiley, owed its origin to solitary sex. Yet the source given on page 48 of Russian Roulette appears impeccable. Describing the early days of the Secret Intelligence Service under Captain Mansfield Cumming, generally known as C, when a desperate search was being made to discover a secure means of communicating clandestine information, Giles Milton quotes the Q of the era, ‘I shall never forget C’s delight at the announcement that one of his staff had found out that semen would not respond to iodine vapour.’

Since the author also asserts that C controlled up to 1,000 operatives, it is difficult not to let one’s eyes widen a little. Could all of them have chosen to send back their secret messages in the same way? After all, how much invisible ink would a spy have to produce in order to transmit a complex report on, say, the strategy of the Comintern to spread communism around the world? Yet apparently undaunted by the demands made upon them, C’s agents buckled down to the business. ‘Our man in Copenhagen, Major Holme, evidently stocked it in a bottle’, Q recalled, ‘for his letter stank to high heaven and we had to tell him that a fresh operation was necessary for each letter.’

Fascinating though this detail is, Russian Roulette has a larger canvas to fill. It aims to show that under C, the embryonic Secret Intellgence Service scotched Lenin’s plan to spread communism into Europe and India. To this end Milton relies heavily on the stash of colourful memoirs by former agents, among them Somerset Maugham, George Hill, Sidney Reilly, and Robert Bruce Lockhart, that appeared in the 1930s. Portraying themselves as masters of disguise and paragons of seduction, they claimed to have stolen secret papers from within the Kremlin, outwitted the Cheka secret police, and manipulated Central Asian rulers like puppets. Cobbled together they offer an entertaining, Scarlet Pimpernellish version of the actual efforts to find out the intentions of the Bolshevik leaders, and later to frustrate their aim of fomenting communist revolution around the world.

Milton is good at conveying the confusion and excitement, but even when they were published, the memoirs which provide much of his material were not taken very seriously: MI 5 prosecuted just one former spy, Compton Mackenzie, for publishing significant information, notably the disclosure that visa offices were used as a front for espionage, but let the other accounts go as entertaining propaganda. There is no reason to think differently now.

Worse still, the matter of the invisible ink undermines Milton’s fundamental purpose. The self-abuser as hero is a difficult ask. Even the clear-cut achievements of someone like Sir Paul Dukes, the only man ever to be knighted for his services to spying, become clouded. It is not so much his success in passing on important information about the Comintern’s intentions that sticks in the memory — ’I wrote mostly at night’, he disclosed in his memoirs, ‘in minute handwriting on tracing paper’ — as the sudden half-confession in the same passage, ‘I made the ink by … oh it doesn’t matter how.’

The subversive nature of this revelation that the founders of the Secret Intelligence Service were actually a bunch of … oh it doesn’t matter whats almost makes one suspect that Russian Roulette might be part of a dirty tricks campaign. At any rate, it is a relief to think that modern technology must have freed their successors from such a debilitating activity. The reports emitted by its agents today presumably arrive at MI6’s hideous green and yellow headquarters in a digitised form to be decoded by computers neatly and odourlessly.

But then, unbidden, comes the thought that since all electronic messages can now be read by both friendly and hostile agencies, really sensitive information must be sent in some other way. A hideous suspicion arises, could our spooks have gone back to an earlier, more secure method, to microdots? Or to wireless? Or, heaven forfend, to something that even iodine vapour cannot crack?